What’s Next in Lithium Batteries?

Current lithium-ion batteries are like democracy: They are the worst option, except for all of the other ones.

But next-generation technologies like lithium-sulfur and lithium-air batteries still have a long way to go before they're ready for laptops and cars, as researchers speaking Wednesday at IBM's annual Almaden Institute at its Almaden labs near San Jose, Calif. made clear.

So for now, lithium-ion is the chemistry of choice for automakers going hybrid and electric, from Toyota, which will use it in its next generation Prius hybrid, to General Motors, which has settled on it for its upcoming Chevy Volt plug-in hybrid.

They're also in prototypes of a plug-in Ford Escape hybrid now being tested on California roads, and could be part of Ford's new line of electric and plug-in hybrid vehicles expected over the next few years, Ted Miller, senior manager of energy storage research at Ford Motor Co., said.

But those batteries – which can give about 30 miles of range before they're discharged – are still far from the ideal battery for Ford and other automakers.

That ideal battery wouldn't just have much longer range – about 100 miles, Miller said. It would also last for about 15 years and cost as little as $20 per kilowatt. At least those are some of the long-range goals of the United States Advanced Battery Consortium, a group formed by Ford, GM and Chrysler.

That's versus current costs of about $1,000 per kilowatt-hour for batteries, or even the target of about $300 per kilowatt-hour once the benefits of mass manufacturing kick in, he said.

"The goals are established to say, how can we make this competitive with existing technology," he said. "To pay this off in a reasonable timeframe, what does that take?"

Beyond the costs, there's the troubling fact that lithium-ion batteries need to be closely controlled to avoid thermal runaway – that is, catching on fire.

"One has to got to increase the energy of existing lithium-ion systems without compromising power and safety," said Michael Thackeray, senior scientist with Argonne National Laboratory.

Safety concerns have led to a "particular nervousness n the community about scaling up lithium ion batteries," he said. The propensity of lithium ion laptop batteries to catch fire has been well-documented.

And as USA Today reported this week, the Air Line Pilots Association, an airline pilots' union, has asked the Federal Aviation Administration decision to ban lithium-ion batteries from flights on safety grounds.

"We need safer materials," Thackeray said. "Today's lithium ion cells are protected by electronic circuitry that is not fail-safe." Possible solutions include coatings that can prevent thermal runaway without interfering with battery efficiency, he noted.

Still, Thackeray told the audience, "Lithium-ion systems offer the best near-term opportunities. If we can improve, even incrementally, the performance of lithium-ion batteries, we'll be making a good start."

But Miller pointed out that lithium-ion technology could still reach a plateau, beyond which it would be necessary to move on with more promising chemical combinations (see Green Light post).

Elton Cairns, a chemical engineering professor with the University of California Berkeley, said that lithium-sulfur batteries could offer a next step forward. Lithium-sulfur cells have a theoretical potential to deliver about 2,600 watt-hours per kilogram, versus lithium-ion's potential of 585 watt-hours per kilogram, he said.

Using sulfur has another advantage, he noted – it's cheap, about 57 cents per kilogram versus $44 per kilogram for cobalt, or $2,25 per kilogram for manganese, to name a few alternative materials.

Research so far has yielded better energy densities than lithium-ion chemistries, but work still continues to increase cycle life and better utilize the sulfur within the battery, he said.

Sion Power makes lithium-sulfur batteries that it claims can store up to 350 watt-hours per kilogram, said Linda Nazar, University of Waterloo in Ontario, Canada.

But she and researchers at University of Waterloo have been researching lithium-sulfur battery technology using nanomaterials that could deliver 550 to 650 watt-hours per kilogram, she said.

An indirect way around the lithium problem could lay in things like inductive charging, which allow the cars to charge while driving. Nissan is researching this. In-flight charging would allow car makers to reduce the size of the battery pack.

Electric transportation "doesn't necessarily mean a battery in the vehicle," said Daniel Sperling, a professor of civil engineering and the founder of the Institute for Transportation Studies at UC Davis. The 16 kilowatt hour battery in the GM Volt might just be an anomaly. In the future, electric cars or plug-in hybrids might come with 2 to 4 kilowatt hour batteries.

Then there are lithium-air batteries, sometimes described as the "holy grail" of battery chemistries, Thackeray said. That's because they offer the theoretical promise of delivering about 10 times the energy density of lithium-ion batteries by exposing metal and an electrolyte to oxygen to release energy.

Some researchers believe that lithium-air batteries using ambient air could achieve energy densities equivalent to that of gasoline, noted Winfried Wilcke, IBM Program Director at the Almaden Institute.

But as Cairns noted, lithium-air batteries might be considered a "generation after next" technology, given the steps that remain between theory and practical application. One big problem is that it's difficult to reverse the reaction that provides power, making recharging a challenge.

Some key problems include finding the right catalysts to reverse the chemical reaction at low enough energy levels, as well as advances in nanotechnology to distribute that catalyst close enough to the metals.

These more advanced batteries may also require three to four times as much lithium as current batteries, which adds cost. Current batteries are actually quite efficient, utilizing almost all of the metal. Even with the additional demand ofr lithium, Ford's Miller said enough lithium carbonate exists in the proven reserves for billions of electric vehicles. "Abundant reserves exist," he said.